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The more cities spend on bike infrastructure, the more important it becomes to make sure that money is spent wisely. One way to measure success in this area is to lay down bike lanes or paths and see if ridership grows. Another is simply to ask riders what facilities they prefer. Both approaches have their drawbacks: The former assumes transportation officials know best and relies on correlations that hopefully reflect causations; the latter may put too much emphasis on hypothetical options and not enough on actual behavior.

A potentially more instructive way to see what riders want from a bike route is to follow riders, in real-time, as they choose a bike route. A trio of transportation researchers at Portland State University -- Joseph Broach, Jennifer Dill and John Gliebe, recently did just that. In an upcoming issue of Transportation Research Part A, Broach and company report a series of nuanced rider preferences that could help designers create more comprehensive bike facilities and help cities implement these facilities more efficiently.

The researchers selected 164 experienced riders in the metropolitan Portland area and clipped a G.P.S. unit to their bikes. The G.P.S. network was rigged to follow them no matter where they might go — from major streets to informal cut-throughs — and to document route details, such as overpasses. Broach and colleagues also worked with Oregon Metro and the city of Portland to gather information on traffic volumes, turns, elevations, bike infrastructure, intersection details in various corridors.

Altogether the researchers compiled data on nearly 1,450 actual bike trips. (They tracked commutes and non-commutes, but not pure recreational riding.) But the information on where riders went wasn't terribly useful unless the researchers also knew where riders hadn't gone. So for every trip they came up with an average of about 20 alternatives, to see if they could determine what riders really looked for in a route ...